Educational technique needs a philosophy, which is a matter of faith rather than of science. - Hans Freudenthal

No statistician present at this moment will have been in doubt about the meaning of my words when I mentioned the common statistical model. It must be a stochastic device producing random results. Tossing coins or a dice or playing at cards are not flexible enough. The most general chance instrument is the urn filled with balls of different colours or with tickets bearing some ciphers or letters. This model is continuously used in our courses as a didactic tool, and in our statistical analyses as a means of translating realistic problems into mathematical ones. In statistical language " urn model " is a standard expression.

Angles are measured by arcs, such that 360° and 2π correspond to each other.

Learners should be allowed to find their own levels and explore the paths leading there with as much and as little guidance as each particular case requires.